U.S. patent application number 13/108661 was filed with the patent office on 2011-09-08 for integrated bias circuitry for ultrasound imaging devices configured to image the interior of a living being.
This patent application is currently assigned to Scimed Life Systems, Inc.. Invention is credited to Jon M. Knight.
Application Number | 20110218442 13/108661 |
Document ID | / |
Family ID | 36181670 |
Filed Date | 2011-09-08 |
United States Patent
Application |
20110218442 |
Kind Code |
A1 |
Knight; Jon M. |
September 8, 2011 |
INTEGRATED BIAS CIRCUITRY FOR ULTRASOUND IMAGING DEVICES CONFIGURED
TO IMAGE THE INTERIOR OF A LIVING BEING
Abstract
The systems and methods described herein allow for the
application of a bias voltage to one or more transducers
implemented within a medical ultrasound imaging system. Bias
circuitry is placed within an imaging device and used to apply a DC
bias to one or more transducers requiring a DC bias to operate. The
one or more transducers can be fabricated in a semiconductor
manufacturing process and integrated with the bias circuitry on a
common semiconductor substrate. Also provided is a method for
operating the one or more transducers and bias circuitry using a
communication channel having two signal lines.
Inventors: |
Knight; Jon M.; (Pleasanton,
CA) |
Assignee: |
Scimed Life Systems, Inc.
Maple Grove
MN
|
Family ID: |
36181670 |
Appl. No.: |
13/108661 |
Filed: |
May 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10966594 |
Oct 14, 2004 |
7967754 |
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13108661 |
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Current U.S.
Class: |
600/459 |
Current CPC
Class: |
B06B 1/0292 20130101;
A61B 8/12 20130101; G01S 15/8906 20130101 |
Class at
Publication: |
600/459 |
International
Class: |
A61B 8/14 20060101
A61B008/14 |
Claims
1. A medical imaging system, comprising: an imaging device
configured and arranged to be insertable into an intravascular
portion of a living being and to image the interior of the living
being, the imaging device comprising: an ultrasound transducer; and
bias circuitry electrically coupled with the transducer and
configured and arranged to electrically bias the transducer; a
driveshaft coupled to the imaging device and configured and
arranged for rotating the imaging device; a signal line located
along the driveshaft and coupled to both the ultrasound transducer
and the bias circuitry and configured and arranged for delivery of
both a transducer drive signal to the transducer and a charge to
the bias circuitry; an image processing system configured and
arranged to provide the transducer drive signal and the charge for
the bias circuitry; and a coupling device configured and arranged
to inductively couple the signal line to the image processing
system, wherein the image processing system is configured and
arranged to provide the charge for the bias circuitry using a
signal which appears as an AC signal to the coupling device.
2. The system of claim 1, wherein the transducer includes a
capacitive micromachined ultrasound transducer (CMUT).
3. The system of claim 2, wherein the bias circuitry is integrated
with the CMUT on a common semiconductor substrate.
4. The system of claim 1, wherein the transducer is one of a
plurality of transducers within a transducer array.
5. The system of claim 1, wherein the bias circuitry comprises a
charge pump.
6. The system of claim 1, wherein the imaging device comprises
rectification circuitry.
7. The system of claim 1, wherein the bias circuitry is configured
and arranged to control the bias voltage.
8. The system of claim 7, wherein the bias circuitry comprises
charge limiting circuitry configured to control the bias
voltage.
9. The system of claim 1, wherein the image processing system is
configured and arranged to provide the charge for the bias
circuitry using a series of DC pulses provided in a single imaging
cycle.
10. The system of claim 1, wherein the image processing system is
configured and arranged to output the transducer drive signal to
the transducer via the signal line during a first time period,
receive an echo signal during a second time period, and output the
charge for the bias circuitry via the signal line during a third
time period, wherein the second time period is after the first time
period and the third time period is after the second time period
and wherein the first time period, the second time period, and the
third time period are in a single imaging cycle.
11. The system of claim 10, wherein the bias circuitry comprises a
charge pump and the amplitude of the bias signal is below an
excitement threshold for the transducer.
12. The system of claim 10, wherein the image processing system is
further configured to output a bias signal during a fourth time
period, longer than the third time period and prior to the first
time period.
13. The system of claim 12, wherein the bias signal output during
the fourth time period is configured to initialize the charge
pump.
14. A intravascular ultrasound imaging system, comprising: an
imaging device configured and arranged to be insertable into an
intravascular portion of a living being and to image the interior
of the living being, the imaging device comprising: an ultrasound
transducer; and bias circuitry electrically coupled with the
transducer and configured and arranged to electrically bias the
transducer; a driveshaft coupled to the imaging device and
configured and arranged for rotating the imaging device; an image
processing system configured and arranged to output a transducer
drive signal during a first time period, receive an echo signal
during a second time period and output a bias signal during a third
time period, wherein the second time period is after the first time
period and the third time period is after the second time period
and wherein the first time period, the second time period, and the
third time period are in a single imaging cycle; a signal line
located along the driveshaft and coupled to the image processing
system, the ultrasound transducer, and the bias circuitry and
configured and arranged for transmission of the transducer drive
signal, the echo signal, and the bias signal; wherein the
transducer drive signal is configured and arranged to cause a
transducer to generate an ultrasound pulse, the echo signal is
representative of an echo received by the transducer and the bias
signal is configured and arranged to provide electrical charge to
the bias circuitry.
15. The system of claim 14, wherein the bias signal is a DC
signal.
16. The system of claim 14, wherein the bias signal is a series of
DC pulses.
17. The system of claim 14, wherein the image processing system is
further configured to output the bias signal during a fourth time
period, longer than the third time period and prior to the first
time period.
18. The system of claim 17, wherein the bias circuitry comprises a
charge pump and where the bias signal output during the fourth time
period is configured to initialize the charge pump.
19. The system of claim 14, wherein the transducer comprises a
capacitive micromachined ultrasound transducer (CMUT) and the bias
circuitry is integrated with the CMUT on a common semiconductor
substrate.
20. The system of claim 14, wherein the bias circuitry comprises
charge limiting circuitry configured to control the bias voltage.
Description
FIELD OF THE INVENTION
[0001] The systems and methods relate generally to the use of bias
circuitry for biasing an ultrasound imaging device in an
intravascular ultrasound imaging system.
BACKGROUND INFORMATION
[0002] To generate an image using a medical ultrasound imaging
system, such as an intravascular ultrasound (IVUS) or intracardiac
echocardiography (ICE) imaging system, an ultrasound imaging
device, typically including one or more transducers, is located on
or within an intravascular device, such as a catheter and the like.
The intravascular device is navigated into the body and the imaging
device is used to image the desired body tissue. To do this, the
transducer generates and transmits an ultrasound pulse into the
body tissue. As this pulse strikes various layers of body tissue,
echoes are reflected back to and received by the transducer. The
transducer generates an electrical output signal representative of
the strength of the received echo and outputs this signal to an
image processing system. The image processing system processes the
signal and uses it to form an image of the body tissue.
[0003] Conventionally, ultrasound transducers have been made of
piezoelectric materials which require ceramic manufacturing
technologies which are vastly different from those used to
manufacture other components in an ultrasound imaging system, which
are typically semiconductor-based. Piezoelectric transducers
typically have a narrow bandwidth which limits the depth of tissue
that can be imaged.
[0004] Recently, a new type of transducer has been developed
capable of fabrication with semiconductor-based processing
technologies. Capacitive micromachined ultrasonic transducers
(CMUTs) were designed to answer a need to mass fabricate medical,
ultrasound transducers using the very same semiconductor
manufacturing processes used to fabricate the other parts of an
external ultrasound imaging system. CMUTs are typically much
smaller than piezoelectric transducers (on the order of 10 to 100
microns in size) and have a larger bandwidth.
[0005] A typical CMUT includes a drumhead structure suspended over
a substrate in a manner to allow two-way conversion between a
mechanical wave and an electrical signal through modulation of a
capacitive charge on the drumhead. To deliver an ultrasound pulse,
the capacitive charge on the drumhead, measured relative to a
substrate electrode, is modulated by delivery of an electrical
pulse to the drumhead. The delivery of this pulse causes the
drumhead to vibrate and thereby transmit an ultrasound wave.
Likewise, in the receiving mode, the impact of the echo on the
drumhead modulates the capacitance and results in an electrical
signal representative of the strength of the received echo.
[0006] CMUT devices are not currently used in IVUS imaging systems:
One reason for this is because in order to operate, the CMUT needs
a constant bias voltage that is carefully controlled so as to
maintain high transducer sensitivity without short-circuiting the
transducer's capacitance. Accordingly, there is a need for systems
and methods for applying this bias voltage to CMUT devices in
intravascular ultrasound imaging systems.
SUMMARY
[0007] The systems and methods described herein provide for an
imaging system having bias circuitry for applying a bias voltage to
one or more transducers. In one example embodiment, the imaging
system includes an imaging device insertable into a living being
and configured to image the interior of the living being. The
imaging device includes an ultrasound transducer and bias circuitry
electrically coupled with the transducer and configured to
electrically bias the transducer. The imaging device can be coupled
with a rotatable driveshaft and communicatively coupled with an
image processing system. The image processing system can be
configured to output a transducer drive signal to the transducer
over a signal line located along the driveshaft and supply charge
to the bias circuitry over the same signal line. Preferably, the
transducer is CMUT capable of fabrication in a semiconductor-based
manufacturing process. In one embodiment, the transducer is a CMUT
and is integrated with the bias circuitry on a common semiconductor
substrate. The bias circuitry can include a charge pump for
accumulating the bias voltage and also charge limiting circuitry
for controlling the bias voltage.
[0008] The systems and methods described herein also provide for an
image processing system configured to operate an imaging device
having bias circuitry. In one example embodiment, the image
processing system can be configured to output a transducer drive
signal during a first time period, receive a transducer output
signal during a second time period and output a bias signal during
a third time period. The transducer drive signal can be configured
to cause a transducer within the imaging device to generate an
ultrasound pulse. The transducer output signal is preferably
representative of an echo received by the transducer. The bias
signal can be configured to provide electrical charge to bias
circuitry coupled with the transducer.
[0009] The systems and methods described herein also provide for a
method of ultrasound imaging with an image processing system. In
one example embodiment, the method includes outputting a transducer
drive signal during a first time period, where the transducer drive
signal is configured to cause a transducer to transmit an
ultrasound pulse. The method also includes receiving a transducer
output signal during a second time period following the first time
period, where the transducer output signal is representative of an
echo received by the transducer, and outputting a bias signal
during a third time period following the second time period, where
the bias signal is configured to provide charge to bias circuitry.
In another example embodiment, the method can include outputting a
second bias signal during a fourth time period prior to the first
time period, where the second bias signal output during the fourth
time period is configured to initialize the bias circuitry. The
fourth time period can also be longer than the third time
period.
[0010] Other systems, methods, features and advantages of the
invention will be or will become apparent to one with skill in the
art upon examination of the following figures and detailed
description. It is intended that all such additional systems,
methods, features and advantages be included within this
description, be within the scope of the invention, and be protected
by the accompanying claims. It is also intended that the invention
is not limited to require the details of the example
embodiments.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The details of the invention, including fabrication,
structure and operation, may be gleaned in part by study of the
accompanying figures, in which like reference numerals refer to
like segments.
[0012] FIG. 1 is a schematic view depicting an example embodiment
of an IVUS imaging system.
[0013] FIG. 2 is a perspective view depicting another example
embodiment of an IVUS imaging system.
[0014] FIGS. 3A-B are cross-sectional views depicting an example
embodiment of a CMUT.
[0015] FIG. 4 is a block diagram depicting an example embodiment of
an IVUS imaging device.
[0016] FIG. 5 is a timing diagram depicting example output signals
from an image processing system.
[0017] FIG. 6 is a flow diagram depicting a method of operating an
imaging device with an image processing system.
DETAILED DESCRIPTION
[0018] The systems and methods described herein allow the
application of a bias voltage to one or more transducers
implemented within an imaging system. FIG. 1 depicts one example
embodiment of an imaging system 100 having bias circuitry 102.
Preferably, the imaging system 100 is an IVUS imaging system. Here,
an intravascular medical device 104, such as a catheter and the
like, is communicatively coupled with an image processing system
106. Catheter 104 is preferably configured to image the interior of
a living being, such as a body chamber or body lumen and the like.
Catheter 104 preferably includes a rotatable driveshaft 108 with an
imaging device 110 coupled thereto. In this embodiment, the imaging
device 110 is mounted on the distal end 111 of the driveshaft 108.
The catheter 104 also preferably includes an elongate outer sheath
(not shown) having an inner lumen for slidably receiving the
driveshaft 108 and imaging device 110.
[0019] To perform an imaging procedure of, for example, a blood
vessel, the catheter 104 can be inserted into the blood vessel and
navigated into proximity with the desired imaging location. Once in
position, the driveshaft 108 is rotated and the imaging device 110
is used to image the blood vessel by continuously transmitting
ultrasound pulses and receiving echoes generated as the ultrasound
pulse travels through the vessel tissue. Imaging device 110 outputs
an output signal representative of the strength of the received
echo over communication channel 140 to image processing system 120,
where the signal can be processed and formed into an image of the
blood vessel and surrounding body tissue.
[0020] A coupling device 130 can be used to couple the stationary
image processing system 120 with the rotatable driveshaft 108. In
one embodiment, coupling device 130 is an inductive coupling
configured to transfer communication signals, such as the imaging
device output signal and the transducer drive signal, between image
processing system 120 and communication channel 140.
[0021] In this embodiment, the imaging device 110 includes one or
more transducers 101 requiring a bias voltage for operation, such
as a CMUT and the like. The imaging device 101 can operate with a
single transducer 101 or with a transducer array having multiple
transducers 101. Each transducer 101 is preferably fabricated using
a semiconductor-based manufacturing technique, although any
fabrication technique can be used. For ease of discussion, the
transducer 101 will be described herein as a CMUT; however, one of
skill in the art will readily recognize that the systems and
methods described herein can be used with any transducer 101
requiring a bias voltage, such as other types of micromachined
ultrasound transducers (MUTs) and the like. Accordingly, the
systems and methods are not limited solely to the use of CMUT
devices.
[0022] The imaging device 110 also includes bias circuitry 102 for
applying a DC voltage bias to the CMUT 101. Preferably, the CMUT
101 and bias circuitry 102 are integrated together. FIG. 2 is a
perspective view depicting a CMUT array 202 integrated with bias
circuitry 102 on a common semiconductor substrate 204, such as
Silicon, Gallium Arsenide (GaAs) and the like. The integrated CMUT
array 202 and bias circuitry 102 are located within housing 208 and
mounted on the distal end 111 of driveshaft 108. Housing 208
preferably includes an imaging window 210, which can be either an
open portion of the housing 208 or a window formed from a material
that does not significantly impede the transmission or reception of
ultrasound signals. Although not depicted here, the integrated CMUT
array 202 and bias circuitry 102 can be packaged using any desired
packaging technique in order to provide protection, ease of
mounting within housing 208 or for any other desired purpose.
[0023] As mentioned above, CMUTs 101 are typically fabricated using
semiconductor-based manufacturing processes on a semiconductor
substrate 204. Preferably, the bias circuitry 102 is integrally
fabricated on the same substrate 204 as the. CMUT 101. CMUT 101 and
bias circuitry 102 can be fabricated using the same process flow or
in different process flows. In embodiments having a CMUT array 202,
bias circuitry 101 can be configured to bias each individual CMUT
101 in the array 202 or multiple bias circuits 101 can be provided
to bias each CMUT separately. The integration of bias circuitry 102
with CMUT 101 allows for improved performance of the imaging device
110 while at the same time making fabrication of the imaging device
easier and less costly. Although integration of CMUT 101 and bias
circuitry 102 on common substrate 204 is preferred, it should be
understood that the systems and methods described herein are not
limited to such. For instance, CMUT 101 and bias circuitry 102 can
be fabricated as discrete components and packaged together, or
fabricated and packaged discretely. Furthermore, CMUT 101 and bias
circuitry 102 are not required to be housed together within housing
208, and in fact can be positioned in any desired location within
catheter 104.
[0024] FIGS. 3A-B are cross-sectional views depicting an example
embodiment of a CMUT 101. FIG. 3A depicts an unbiased CMUT 101
having a flexible upper electrode 302 suspended over a lower
electrode 304 both of which are fabricated on substrate 204. The
flexible upper electrode 302 is also referred to in some contexts
as a "drumhead." Located between electrodes 302 and 304 is an
insulator layer 306, composed of an insulating material such as
silicon oxide or the like. Preferably, upper electrode 302 and
lower electrode 304 are separated by a gap 308. Upper electrode 302
can completely encase gap 308 on all sides, in which case gap 308
is preferably a vacuum.
[0025] FIG. 3B depicts CMUT 101 after a DC bias voltage 310 is
applied across electrodes 302 and 304. DC bias voltage 310 builds a
capacitive charge on the electrodes 302 and 304 causing upper
electrode 302 to flex, or deflect, downwards towards lower
electrode 304 in direction 312. The application of a drive signal,
such as an electrical pulse or an AC signal, to the biased CMUT 101
modulates the degree of deflection of upper electrode 302 causing
the generation of an ultrasound pulse, which can be used to image
body tissue. Conversely, when an ultrasound pulse, such as a
received echo, impacts the biased CMUT 101, an electrical pulse
corresponding to the strength of the received echo is generated. In
this manner, CMUT 101 can be used to transmit and receive
ultrasound signals in IVUS imaging system 100.
[0026] The actual DC bias voltage 310 and drive signal levels are
dependent on the needs of the application and the characteristics
of each CMUT 101. In general, a larger DC bias voltage 310 will
translate into the generation of a stronger ultrasound pulse. In
addition, the bias voltage 310 can also be a factor in determining
the frequency of the generated ultrasound pulse. In some
applications, the DC bias voltage 310 can be approximately 100-150
volts, while the drive signal level can be 75 volts or more. It
should be understood that these values are provided solely as
examples and any signal levels can be used as desired.
[0027] The design and fabrication of CMUT devices is discussed
further in Percin, G. and B. Khuri-Yakub, Piezoelectrically
actuated flextensional micromachined ultrasound transducers,
Ultrasonics, 2002. 40(1-8): p. 441-8, Percin, G. and B.
Khuri-Yakub, Piezoelectrically actuated flextensional micromachined
ultrasound transducers-II: fabrication and experiments, IEEE Trans
Ultrason Ferroelectr Freq Control, 2002. 49(5): p. 585-95 and
Percin, G. and B. Khuri-Yakub, Piezoelectrically actuated
flextensional micromachined ultrasound transducers-I: theory, IEEE
Trans Ultrason Ferroelectr Freq Control, 2002. 49(5): p. 573-84,
each of which is fully incorporated by reference herein.
[0028] FIG. 4 depicts another example embodiment of imaging device
110. In this embodiment, imaging device 110 includes CMUT array
202, bias circuitry 102 and rectification circuit 402, all of which
are preferably integrated on common substrate 204. Bias circuitry
102 includes a signal blocking circuit 404 and a charge pump 406
configured to apply the DC bias voltage 310 to the array 202. A
bias signal is preferably transmitted along communication channel
140 to supply charge to charge pump 404 and generate the DC bias
voltage level 310 necessary to properly bias the CMUTs 101 within
array 202. The design and implementation of charge pumps are well
known to those of skill in the art and any type of charge pump can
be used. The charge pump preferably includes a charge storage unit,
such as a switched capacitor bank and the like. Furthermore, DC
bias circuitry 102 can be any circuitry configured to control and
apply a DC bids voltage including, but not limited to, a charge
pump 404.
[0029] In embodiments where coupling device 130 uses an inductive
or other non-physical electrical coupling to transfer AC signals
between image processing system 120 and imaging device 110, the
bias signal is preferably a series of DC pulses that appear as an
AC signal to the coupling device 130. In embodiments where coupling
device 130 uses a physical coupling, such as a brush/contact
combination, the bias signal can be a pure DC signal if
desired.
[0030] Rectification circuit 402 can be used to isolate the charge
built up within imaging device 110. Because system 100 can be used
primarily for medical imaging within living beings, rectification
circuit 402 guards against the risk of electrical shock or other
hazards to the patient or the circuitry of system 100.
Specifically, rectification 402 can be used to block or prevent
signals, such as the charge in charge pump 406 or array 202, from
propagating onto communication channel 140. Any type of
rectification circuitry can be used, such as one or more diodes and
the like. Signal blocking circuit 404 can be used to block the CMUT
drive signal from propagating to charge pump 406. One of skill in
the art will readily recognize that FIG. 4 depicts one of many
possible different circuit layouts for imaging device 110 and,
accordingly, the systems and methods described herein are not
limited to any one layout or circuit design.
[0031] Communication channel 140 can include any number of signal
lines or transmission lines as needed. For example, communication
channel can include a ground signal line, a CMUT drive signal line
and a bias circuitry bias signal line. However, because system 100
is preferably used for intravascular applications, the width of
catheter 104 can be a limiting factor preventing advancement
through narrow vasculature. Thus, because each additional signal
line generally adds width to the driveshaft 108, even if the
driveshaft 108 itself is used as a signal line, the number of
signal lines used in communication channel 140 is preferably
minimized. Typical IVUS imaging systems use a communication channel
140 that includes two signal lines which can be used to transfer
single-ended or differential signals.
[0032] In order to use two signal lines to transfer the transducer
drive signal, the bias signal and the transducer output signal, the
systems and methods described herein use a segmented timing regime.
FIG. 5 is a timing diagram depicting the signals output from image
processing system 120 according to one example embodiment of the
segmented timing regime. In this embodiment, imaging device 110 is
rotated to image a cross-section of the body lumen. The
transmission of an ultrasound pulse followed by the reception of
the resulting echo signals is referred to herein as an imaging
cycle. System 100 can be configured to perform a predetermined
number of imaging cycles for every rotation, with each imaging
cycle being performed at a separate angular location, or range of
angular locations. For instance, in one embodiment, imaging device
110 performs 360 imaging cycles in each rotation, with one imaging
cycle being performed at an angular location located one degree
apart.
[0033] Preferably, imaging device 110 is rotated at a rate such
that the time required to perform an imaging cycle is less than the
time required to rotate the imaging device 110 from one angular
location to the next. For example, in FIG. 5, at time T.sub.0 the
imaging device 110 is at a first angular location and at time
T.sub.4 the imaging device 110 has been rotated to a second angular
position. The imaging cycle for the first angular location occurs
between times T.sub.0 and T.sub.2. More specifically, the CMUT
drive signal 502 is transmitted from image processing system 120 to
the array 202 from time T.sub.0 to time T.sub.1 in order to cause
each individual CMUT 101 to transmit an ultrasound pulse. From time
T.sub.1 to time T.sub.2, image processing system 120 is in a
receiving period 502 awaiting any output signals generated by the
array 202 in response to received echoes. This leaves the remaining
time from T.sub.2 to T.sub.4 unused in any imaging cycle.
[0034] During the time from T.sub.2 to T.sub.3, the image
processing system 120 preferably transmits the bias signal 504 to
bias circuitry 102. At time T.sub.4, the image processing system
120 transmits another drive signal 501 to initiate the imaging
cycle at the next angular location. In one example embodiment, the
time period from T.sub.0 to T.sub.4 is 130 microseconds, with the
time period from T.sub.0 to T.sub.1 being approximately 50
nanoseconds, the time period from T.sub.1 to T.sub.2 being
approximately 20 microseconds and the time period from T.sub.2 to
T.sub.3 being approximately 100 microseconds. These times are
included as examples only and in no way limit the systems and
methods described herein.
[0035] Bias circuitry 102 can use the bias signal to generate the
required DC bias voltage 310. The amplitude of the bias signal 504
is preferably lower than the CMUT 101 excitement threshold where
the CMUT 101 produces an ultrasound pulse. In some applications,
small ultrasound pulses may be tolerable if, for instance, the
small ultrasound pulse does not interfere with the subsequent
imaging cycle. The term "excitement threshold" as used herein,
refers to the signal level which causes one or more transducers to
generate ultrasound pulses at a level sufficient to interfere with
an imaging cycle. In one embodiment, the excitement threshold can
be 75 volts and the bias signal 504 is maintained at 70 volts,
while the drive signal 501 is 125 volts. These values are solely
for example and in no way limit the systems and methods described
herein. As mentioned above, the bias signal can be a series of DC
pulses instead of a continuous DC pulse in order to propagate
through coupling device 130, if needed. Also, it should be
understood that any waveforms can be used for drive signal 501 and
bias signal 504.
[0036] The generation of bias signal 504 and drive signal 501, as
well as the proper timing for doing so, can be controlled by the
image processing system 120. Preferably, the bias circuitry 102 is
configured to limit the charge build up so that the bias signal 504
does not cause bias circuitry 102 to apply a DC bias voltage 310
that is too high. This can be performed through charge limiting
circuitry well known to those of skill in the art. Also, in certain
applications, multiple charging cycles may be needed before bias
circuitry 102 can apply the proper. DC bias voltage 310.
Alternatively, in another embodiment the image processing system
120 can be configured to output the bias signal prior to the
commencement of imaging in order to charge up, or initialize, the
bias circuitry 102. In this embodiment, the length of the
initialization period can be as long as needed to charge the bias
circuitry 102. Preferably, the bias circuitry 102 is designed to be
low leakage so that once the proper DC bias voltage 310 is reached,
minimal subsequent charging is needed.
[0037] FIG. 6 is a flow chart depicting a method 600 of operating
the imaging device 110 with an image processing system 120 in an
embodiment where communication channel 140 has only two signal
lines available. At 604, the imaging device 110 is rotated to a
first angular location. At 606, the image processing system 120
outputs a transducer drive signal 501 during a first time period to
cause one or more CMUTs 101 to generate an ultrasound pulse. At
608, the image processing system 120 listens for any transducer
output signals representative of the strength of an echo received
by any CMUT 101 during a second time period. At 610, the image
processing system 120 outputs a bias signal 504 during a third time
period to charge the bias circuitry 102.
[0038] In addition, method 600 can also include an optional
initialization process, referenced as 602, where the image
processing system 120 can output bias signal 504 during a fourth
time period, preferably in order to initialize the bias circuitry
102. Then, the method returns to step 604 and rotates to the next
angular position and repeats steps 606-610. This process continues
until imaging at all of the desired angular locations has taken
place. The rotation of imaging device is preferably continuous but
performed at such a rate where the rotation that occurs during the
imaging cycle is negligible for the needs of the application.
[0039] In the foregoing specification, the invention has been
described with to specific embodiments thereof. It will, however,
be evident that various modifications and changes may be made
thereto without departing from the broader spirit and scope of the
invention. For example, each feature of one embodiment can be mixed
and matched with other features shown in other embodiments, and the
sequence of steps shown in a flowchart may be changed. Features and
processes known to those of ordinary skill may similarly be
incorporated as desired. Additionally and obviously, features may
be added or subtracted as desired. Accordingly, the invention is
not to be restricted except in light of the attached claims and
their equivalents.
* * * * *